1. Technical Field
This invention relates to lighting and more specifically to edge light backlights for flat panel displays or luminaires.
2. Background Art
One structure for a backlight source is described in J. C. Wilson U.S. Pat. No. 6,299,328 B1, Oct. 9, 2001. As seen in FIGS. 1 and 2, which correspond to figures of the Wilson patent, a tubular light source 10, such as a fluorescent bulb, is positioned axially within a tubular reflective cavity 11 which has a linear slit opening 15 which allows light to pass from the light source 10 to a cylindrical rod lens 14 positioned in the opening. The cylindrical rod lens 14 may advantageously be positioned in an external waveguide that takes the light from the cylindrical rod lens to the equipment, such as a display, which is to be illuminated.
In the Wilson arrangement in order to achieve higher output irradiance and radiance for the linear illumination system, the linear slit opening 15 should have as large a width as possible, being constrained only to be less than the maximum inside width of the tubular cavity 11. The axes of the lamp 10, the tubular cavity 11, and the rod lens 14 are parallel. The cylindrical rod lens 14 projects the light into the associated waveguide in a single projection lobe having a wide angular range angular range of ±θ2. More specifically, the cylindrical rod lens 14 receives light input through the linear slit opening 15 and projects this light towards a waveguide light input edge. The cylindrical form of the rod lens 14 collimates its light input from the tube enclosure only in the Y-Z plane. Accordingly the profile of light projected in the X-Z plane is uncollimated, which gives it a much wider angular distribution than the profile of the collimated component in the Y-Z plane. To minimize the angular span of the profile in the Y-Z plane for a given slit width, the tube enclosure's linear slit opening 15 should occupy the focal surface of the rod lens 14.
The light beams from this single lobe are reflected by the internal reflective surfaces of the waveguide. However, the efficiency of the light being transmitted through the waveguide is dependent on the number of reflections within the waveguide.
Accordingly, there is a need to increase the amount of luminous flux delivered to edge lit backlights and the luminous efficiency (lumens output per watt input) of the source system input to the backlight in the type of structure taught by the Wilson patent.